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Federal regulators are proposing to designate 70,600 square miles of ocean off the West Coast as "critical habitat" for endangered Pacific leatherback sea turtles, a move that would put the United States at the forefront of protecting the world's largest marine turtle.

The designation would mean more review of projects such as liquefied natural gas terminals and wave energy plants. The The National Oceanic and Atmospheric Administration Fisheries Service would scrutinize the potential effects not only on the turtles but on jellyfish and other West Coast prey that the leatherbacks migrate thousands of miles to feed on.

The proposal for critical habitat designation covers the relatively near-shore ocean along all of Washington's coast, and along Oregon's coast from the northern border south to Winchester Bay, where the Umpqua River hits the ocean. It also covers the portion of California's coast from Point Arena, north of San Francisco, to Point Vicente, south of Los Angeles.

The fisheries services proposes to exclude waters off the stretch of Oregon and California coast from Winchester Bay south to Point Arena. It said the area includes "great densities" of jellyfish but that leatherback use is "limited" and the conservation benefits don't outweigh the potential costs.

The environmental groups that petitioned and sued the government to obtain a critical habitat listing -- Oceana, the Center for Biological Diversity and the Turtle Island Restoration Network -- said leatherbacks consistently use that area off Oregon and California and it should be included as critical habitat, too.

They also questioned the decision to not focus on turtles accidentally caught by fishermen using drift nets or long lines to catch swordfish, thresher sharks and tuna. Accidental "bycatch" is a leading cause of death for the turtles, the groups said.

The U.S. government has severely restricted those types of fishing during leatherback migration and feeding periods. But including fishing gear as a threat to turtles in a habitat designation would further boost scrutiny of fisheries, said Ben Enticknap, Oceana's Pacific project manager.

Nonetheless, Enticknap said the proposed critical habitat designation, when combined with the existing fishing restrictions, would be "a huge step in the right direction."

"The United States would be doing a lot for the leatherbacks off the West Coast and setting a policy precedent for the world," he said.

The leatherbacks can grow up to 9 feet long and weigh up to 1,200 pounds. They lay eggs on tropical beaches on islands in Indonesia, Malaysia and elsewhere in the western Pacific and migrate to the West Coast in their search for food, traveling up to 12,000 miles -- the largest range of any reptile.

The threats during the Pacific leatherback's journey include accidental snaring by fishermen, pollution, poaching and ingestion of floating plastic trash, including plastic bags that can look like jellyfish.

Leatherbacks were listed as endangered throughout their range in 1970. Federal biologists estimate there are about 4,000 adult Pacific leatherback females left, with some major nesting rookeries close to extinction.